The condition of the worker at University Medical Center Brackenridge in Austin wasn't immediately available, and it was unclear whether the man in the crane was hurt. Their identities weren't released.
A group of boys from a nearby neighborhood scrambled to the scene after hearing about the crash and said they saw what appeared to be injured people.
The crane's base was in the riverbed when it was attempting to remove the beam, or girder, from the old bridge, Department of Transportation spokesman Marcus Cooper said.
"The momentum of the girder overloaded the crane and the crane fell over," said Cooper.
The crane was performing routine work to remove the old Loop 230 bridge in Bastrop County, Cooper said. The old bridge has been removed piece by piece for months, and what's remaining sits near the new bridge that replaced it.
When the crane toppled on the riverbed, some oil spilled into the river, but Lower Colorado River Authority officials on the scene said the spill was not large. Booms were in place to clean it up.
Smithville is about 45 miles southeast of Austin.
Slideshow archive | ABC13 wireless | Headlines at a glance